Has Topper Mortimer moved on from Vogue-ette Valerie Boster? The financier, who is still technically married to socialite Tinsley Mortimer, was spotted on a date with Meredith Ostrom, the longtime girl friend of Duran Duran key boardist Nick Rhodes. “They had dinner at Brinkley’s [downtown] and then were dancing and canoodling all night at Southside,” a spy says. “They left together.” Topper was recently featured in The Post’s list of the most eligible bachelors in the city.